Is it ensure, insure, or assure?
in anthropology, theory holding that the age of culture traits (elements of a culture) may be determined by examining their distribution over a large geographic area. The hypothesis states that widely distributed traits are older than those more narrowly distributed. It is based on the assumption that traits tend to diffuse outward in a circle from a single centre. Traits at the periphery are believed to have left the centre earlier than those closer to it and are therefore characteristic of an earlier period of the centre